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TCP/IP and WAN

by
Johannes Helmig
[Published on 24 March 2001 / Last Updated on 24 March 2001]

TCP/IP is in most companies now the standard protocol, especially when multiple locations(Offices and/or factories) are connected via a Wide-Area-Network ( WAN ) :

In the headquarter, there will be mostprobably some servers, which need tobe accessed from Remote offices and/or factories (like a mail-server and/or acompany internal webserver ) and/or amain-frame or mini-computer, runninga common accounting system or anEnterprise Resource Planing System( ERP ), which usually are accessed fromthe client-computers via TCP/IP.

The headquarter could be connectedvia fixed lines (provided by WAN providers) to the remote offices and/or factories.Once the routers are setup properly bythe WAN provider, you as a user willnot need to worry about the WAN,you have access to the servers andmain-frame, as long as in all locationsthe systems are properly configuredfor the router/Gateway.

But there is also a special item towatch out for in the remote location when connecting via a modem anda dial-up connection to the Internet :

Once you connect to the Internet,you will loose the connection via theWAN to all the systems in the Headquarter, you will not be able to PING them.

What happened ?

Use in the START-menu the RUN-command to start "winipcfg" andcheck your IP-values of the dial-upconnection (via the modem) to theInternet, which is the "PPP Adapter":Usually, you get an additional Gatewayaddress assigned to you for theInternet connection.All network traffic, also for theinternal communications, will nowbe send to the Internet gateway !

While you are connected, you have now a configuration with multiple routers/gateways, and you will have to give Windows a "helping hand" to tell it, which router/gateway to be used forInternet network traffic and which one for company internal network traffic:you need to use the "ROUTE" command to inform Windows, which gateway to use to accessthe systems in the headquarter (more details on ROUTE in the next section below):

Your system knows now to use the gateway address at 192.168.1.1for internal communication withthe headquarter, while all othercommunications will use thegateway defined by the Internetconnection

A WAN setup with multiple Routers/gateways in a location:

With 2 gateways, you have 2 possibilities:

1) Define one of them as the Default gateway (usually the Internet Gateway) and programthis gateway to pass any network traffic for the headquarter on to the WAN router/gateway.But very often, you as a user or even network administrator do not have access to theinternal routing tables of your router, requiring you to use the 2nd possibility.

2) Define the gateway with the widest range of IP-addresses (usually the Internet Gateway)as your Default gateway and then program your own system to send all other network traffic (for internal communication ) to the WAN router by using the "ROUTE" -command:

The Help-information, as displayed on a WindowsNT4 or Windows2000 system in aCommand-prompt window:

We need to use the "ROUTE ADD"command to program the systemto send all network traffic for theaddress range 192.168.2.0(applying the subnet-mask of255.255.255.0) to the gateway/router at 192.168.1.1

Note: on a Windows NT or Windows2000 system, you can use the option: '-p':which makes the programming persistent: the value will still be programmed after a system reboot.On a Windows 95/98/ME system, you will need to redefine this ROUTE ADD command aftereach reboot, either manually or by entering the command in a batch-file, executed via the STARTUPfolder.

See Also

The Author — Johannes Helmig

Dr.Johannes Helmig is working as Director, Technical Knowledge Management in the Belgium office of Gerber Technology where he is involved in Customer Service and internal training, with special interest in Networking.

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